Power adapters are commonly used for mobile vehicles which are equipped with significant electrical and electronic equipment. A typical example is a boat or recreational vehicle which can be equipped with navigational equipment such as radio and radar, kitchen appliances such as a cooking range and refrigerator, entertainment equipment such as television and stereo, and other such electrical and electronic equipment. When a boat is moored at a dock or the like, electrical power is commonly supplied from a shore or dockside power center, such as a dockside electrical pedestal at the marina, which includes at least two electrical receptacles into which cables from the vessel can be inserted. Such a power center commonly has two or more identical receptacles each supplying 120 volts AC. If all of the equipment aboard the vessel is designed to operate at the same voltage, there is no problem. However, if the craft has 240 volt (or 208 volt) equipment, or if the power distribution system on the craft is a 240 distribution system, the operator of the craft can not simply connect a docking power connector on the craft to the pedestal. For example, equipment such as blower motors, pumps or the like are wired for 208-240 volt power, that equipment may either not operate at all or operate at a low speed and overheat because of improper voltage.
Marinas usually provide separate 120 volt outlets on the pedestal wired from two phases of a two or three phase supply so that appropriate voltages are available for powering the equipment on a craft which requires a 240 volt supply. However, those two or three out-of-phase sources must be connected together in an appropriate manner before they are useful for powering the 240 volt equipment on the craft. Typically, the pedestal simply has the out-of-phase 120 volt sources brought out to separate receptacles, so that they can be used in the ordinary way for powering 120 volt equipment. It is common for a boat owner to make or buy a “Y” adapter with two male plugs at one end to make 120 volt input connections and a single 125/250 volt output connector having female contacts. The 125 volt input connectors are then inserted into the two receptacles on the pedestal and the single 125/250 volt output connector is plugged into the marine vessel ship-to-shore cable set as an input to the receptacle on the vessel. The electrical wiring for the vessel is connected to this receptacle.
Although a Y-adapter can theoretically provide a desired voltage of 120V or 208-240V and current to a vessel from a receptacle, there are a few practical problems with using the Y-adapter in various situations, such as improper connection of the Y-adapter to the power source, potential problems with the wiring of the pedestal power source, problems with the phase of the power supplied to the pedestal, and the like.
As an example of an improper connection of the Y-adapter, when one of the input connectors is inserted into a live socket in the pedestal, live voltage can also appear on the other input connector if precautions are not taken. If the user has his body in contact with the electrical prongs of an unconnected input connector, (s)he is subjected to the danger of receiving an electrical shock.
As another example of potential problems with the pedestal power source, if the electrical sources from the two selected receptacles are not from different phases, or not of a sufficient difference, the output voltage will not be adequate to drive the equipment on the craft. As another example, although with the proper phase difference, additional problems can result if one of the voltage sources is wired with its polarity reversed.
Further, overcurrent and overtemperature situations can also cause serious problems. For example, as the adapter plugs into a 50 A rated receptacle, it is a common misconception that the reverse Y-adapter is rated for 50 A. Although it may operate indefinitely at 50 A, circuit runs, wires and connectors that are rated at 30 A may overheat and have a shortened life.
Although some available technology can fix some of the problems, there are still some problems. For example, it is common in currently available circuit designs for a Y-adapter to place at least one circuit element across the hot terminal of two input connectors or plugs. In this design, a single component fault can cause a shock condition. As another example, some currently available designs have a tendency to buzz at low input voltage conditions and may cause the circuit to chatter or produce intermittent output. Still other problems include a bulky size or a tendency to fail at prolonged relatively high current conditions.